Meteor Blog 17.-18. August: QUEST 226 - The final dive

The time had come for the final dive of underwater robot QUEST-what a success: If taking samples from the wood fall experiment, Videomosaicking or simply watching deep-sea organisms. Cruise leader Antje Boetius describes her impressions of the fascinating Deep Sea at the Westafrican continental margin.

Planetearth Blog

Does the
biodiversity of deep-sea organisms play a role for the climate on Planet Earth?
Questions all about marine research will be answered directly aboard of the
German research vessel Meteor by cruise leader Prof. Antje Boetius and her
crew. In cooperation with the geoportal planeterde.de from 17.08.08 to 24.08.08
they contribute a Science-Blog of
METEOR expedition M76/3 GUINECO – MARUM research of fluid and gas seeps on the
Westafrican continental margin. Technical highlight of the cruise is the
remote-controlled under water robot QUEST4000 by MARUM that will be deployed
for taking fauna and sediments samples and conduction of in situ experiments. Go on a dive down to places no other human
being has ever seen before: explore the fascinating deep-sea fauna and watch
the scientists’ work at gas and fluid seeps deep down on the ocean bottom.

Expedition
M76/3b is a collaboration of MARUM – Center for Marine Environmental Sciences
at Bremen University
and its associated institutes MPI and AWI as well as the French research
institute IFREMER and the University
of Paris.

More Informationen of the Meteor-Blog, an overview of all contributions to the blog and expedition M76/3B:

17.-18. August
2008 (Author: Antje Boetius)

After dive 225 we were facing the same
situation again: the ROV came up with a twisted cable (picture 1). But being so
close to the end of the cruise, our ROV team collected again all their forces
and used the 17 August for another repair phase, to permit a final dive.

Picture 1 -
The cable of ROV QUEST is twisted. Unfortunately such an incidence
is really dangerous for the ROV recovery, and as a
consequence
the cable is cut and re-terminated.

On the 17th we completed some Parasound
transects to the mud volcano area (see BLOG 02.08.2008), and were intrigued by
indications of a gas flare above the pie-shaped mud volcano in an area, which
we had not covered with our video-transect. Unfortunately, the remaining time
was too short to plan further work at these mud volcano structures as well as
at the other interesting geostructures around the so called Diapir area close
to the submarine Congo canyon, as still a few geological samples were needed in
the REGAB area, not to mention the hope for a final dive.

Picture 2 -
The TRACS are colonization experiments offering different surface
materials for larval settlement, such as wood, carbonate and plant
material

All scientists got together in the
afternoon of the 17 August to plan QUEST dive 226. We came up with a list of
tasks easily filling 24 hours and requiring a lift operation. Of course this
was a risk, because a failure during the final dive would have left our
expensive equipment at the deep sea floor. But everybody agreed that we should
use the chance of a long final dive before steaming home, and that chance
should be on our side. The tasks for QUEST dive 226 included deployment of
several profiling instruments, recovery of some experimental moorings, biological
samples, water chemistry and the time-demanding “videomosaicking” in the areas
where we had worked most. This is a special task for the ROV, where it has to
fly at a constant altitude and velocity and known track over the seafloor to
visually map organisms and habitats. Producing visual maps of benthic habitats
is the only way of arriving at quantitative estimates for the areal coverage of
visible structures – for example of the different bivalve species, the
tubeworms, the carbonates. For this task, QUEST is equipped with a high quality
camera looking downwards, to produce video footage and images, which can
subsequently be put together like a “Mosaic”, using the positioning
information. This sounds simple, but is really a complicated endeavor due to
the difficulties of underwater positioning (also see BLOG 07 Aug).

Picture 3 -
Wood is a favored habitat in the deep sea, even if it
does not
belong there. Many animals are specialized in colonizing
tree logs

Summarizing dive 226, it was really a
success. Despite the persisting oil leak, we arrived at a 24 hours dive before
the reserve (also see BLOG of 3 August) and already accepted as new home to
many shrimps (picture 3), which normally prefer tubeworms and mussels as
associates.

Picture 4 -
The microprofiler measures oxygen penetration in the sediment,
here close to the wood log

We even observed a shrimp eating feces of Calyptogena clams, so
these critters seem quite promiscuous in their associations. The microprofiler
was deployed close to the wood (picture 4), as well as really close to a patch
of vesicomyid clams, another risk taking, because the fine microsensors break
easily on the shell of a clam (picture 5). Our Eddy system (also see BLOG of 26
July for explanation of in situ payloads) was placed close to and away from
vesicomyid clams for community respiration measurements (picture 6). Also, we
stopped in the center to watch the beautiful assemblage of organisms in the
dense tubeworm forest (picture 7). A peculiar feature of this habitat is the
attachment of mytilid bivalves to the tubes, as well as the dense colonization
by hydroid polyps.

Picture 6 -
The eddy system records total community respiration in
the
vesicomyid habitat

These are just examples of the fascinating
deep sea life, and dive 226 truly gave us a feeling of how things could have
been hadn’t there be so many technical issues. Again, we were truly grateful to
our ROV team who did not give up and realized this final dive of the GUINECO
mission.